Telephone system.



F. A. STEARN.

TELEPHONE SYSTEM. APPLICATION FILED .IULY 5.1916.

Patented Jail. 22,1918;

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F. A. STEARN.

TELEPHONE SYSTEM.

APPLICATION FILED JULY 5.1916.

Patented J an. 22, 1918.

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F. A.-STEARN.

TELEPHONE SYSTEM. 4

APPLICATION FILED JULY 11916- Patented Jan. 22,1918.

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FRANKLIN A. STEARN, OF EATER/SON, NEW J ERSEY, ASSIGN'OR T0 WESTERN ELECTRIC COMPANY, INCORPORATED, 013 NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE SYSTEM.

Specification of Letters Patent.

men al c as, tiers,

Application filed July 5, 1316. Serial No. 107,540.

tributing to a plurality of operators posi-' tions the calls originated by the telephonelines of the exchange.

,The invention more particularly has to do with a system in which the operation of" the switches that extend the connections of the. calling lines is governed. by selectioncontrolling mechanism that is common both to the switches and to the operators positions to which the connections are to be ex This selection-controlling mechanism is responsive to the engaged or unengaged condition of the various operators positions and acts to direct each call, as it is initiated, to an unengaged operators position.

Heretofore it has been the practice to keep selection-controlling mechanism of this sort constantly under the electrical control of all of the associated operators positions so that it continually keeps established a path for the selection of an available operators position by a call-extending switch. It is the object of this invention so to organize the system that the selection-controlling mechanism is normally inert or quiescent and is made active to establish the selecting path only when one of the associated switches is in readiness to extend a call. This effects a considerable saving of the current flow required in the operation of the system.

'The preferred embodiment of the invention is illustrated in the accompanying drawing, in which Figures 1. 2 and 3, taken together, and with Fig. 1 placed under Fig. 2, and Fig. 3 at the right of Fig. 2, show as much of a complete system as is necessary for an understanding of the manner in which the system is organized and operates. Referring to the drawings, the part of the complete system that is shown comprises a plurality of telephone lines extending from stations A and B to a central otlice, two operators positions O-and 0' each of which is provided with cord circuits 0 for extending connections to called subscribers lines, finder circuits F and F terminating at one end in switches LF and LF for connecting the finder circuits with calling subscribers lines and at the other end in cord selector switches CS and CS for connecting the finder circuits with the connecting circuits of the operators positions, and selection controlling apparatus SC for governing the selection of an idle operators position by an actuated cord selector.

The cord selector switches CS and CS are preferably of the type disclosed in Patent 1,177,044 to J. L. McQuai-rie, issued March 28, 1916. Each switch comprises a longitudinally movable shaft 1 carrying as many sets of brushes 2 as there are groups of stationary terminals to be engaged. To move the shaft and. its sets of brushes up, an extension at thelower end of the shaft is brought into engagement with the con stantly rotating power member 3 by means of an idler wheel operated by the up-drive magnet 34; and to move the shaft down, the extension is brought into engagement with the power member 4 by means of an idler wheel operated by the down-drive magnet 35.

Normally the brushes of each of the sets 2 are held apart so as to clear the associated terminals by means of a separating cam 5 located between the innermost brushes of the set. The cam 5 is rotatably mounted. and when rotated, releases the brushes and permits them to engage the associated terminals. The tripping or releasing of the brushes is controlled by a number of tripmagnates 20, 21. Each of these when energized rotates an associated trip rod 6 that extends transversely to the switch shafts 1 and carries as many tripping yokes 7 as there are finder switches in the'group.

The trip rod in rotating brings all of its tripping yokes 7 into position to operate the brush controlling cams 5 of the corresponding sets of brushes on all of the switches, so that whichever of the selector switches is caused to move up has that set of brushes tripped that corresponds with the particular trip magnet 20, 21, that is at the time energized. When the selector switch that has been in use is returned 00 it IlQrmal posicooperating with the stationary segments.

This commutator'serves to make and break a number of controlling circuits in the various stages of the upward movement of the switch shaft.

The switches LF, and LF, by means of which the finder circuits are brought into connection with the calling lines, may be of the same type as the cord selector switches,

in which case they are supplemented with controlling parts and circuits suitable for their operation; or they may be any other convenient type of switch, such as plugs and spring jacks for establishin connection between the finder circuits and the lines.

For controlling the circuits of the organization there are employed a number of sequence switches which are shown at different points and are designated 200, 300 and 400, respectively, These sequence switches may be of the type disclosed in Patent 1,127,808 issued February. 9, 1915, to Reynolds and Baldwin. Each consists of an electro-magnetically controlled motor or driving mechanism and a number of associated switch contacts. The switch contacts associated with each of the sequence switches are designated 201. to 216 inclusive; those associated with each of the sequence switches 300 are designated 301 to 303 inclusive; and those associated with each of the sequence switches-400 are designated 101 to 114 inclusive. To each of the contacts associated with the various sequence switch cams are applied certain numerals. These numerals in the case of the cams 201, 301 and 401 indicate the only positions of the associated sequence switch in which these particular contacts are open; the numerals applied to allof the other contacts of each sequence switch indicate the only positions of the particular associated switch in which the associated contacts are closed.

The manner in which the system is organized will best be presented in connection with a description of the mode of its operation. It will be assumed that the subscriber at station A initiates a call. The removal of the telephone receiver from itsswitch-.

hook closes a circuit that includes both windings of the line relay 12, the resting contacts of cutoff relay 11 and both limbswhich eander of the calling line to the associated finder circuit F or F. This result may be brought about either directly by energizing the driving mechanism of one or the other of the switches if these are mechanically operated switches, or indirectly by-displaying a signal in response to which a distributing operator may insert a finder circuit plug in the springjack of the calling line if the switches are of that type. The method to be preferred is illustrated in detail in Patout No. 1,247,770, issued to Samuel B. Williams, Jn, November 27, 1917.

Assuming that the circuit of the calling line has been extended to the finder circuit F in one of the manners described, or in any other convenient and well-known way, and that the sequence switch 200 associated with the finder circuit has thereby been moved out of position 4, the apparatus proceeds to select an idle opcrators position and extend the circuit of the calling line to one of the connecting circuits with which the selected position is provided. When the sequence switch reaches position 5, in its movement out of position 4:, it closes a circuit that prepares the selection-controlling mechanism SC for cooperation with the cord selector switch in the immediately following stage of operation of the system. Normally the selectioncontrolling mechanism is inert. and with no current flowing in any part of its circuit net-work. When'the sequence switch 200 reaches position 5, a circuit is closed that extends from battery, through the winding of the relay 55 of the selectioncontrolling apparatus, conductor 71, sequence switch contact. 215 (5 to 8) and to ground. The sequence switch 200 stpps in position 6, in which position the circuit just traced continues closed. When relay of the selection-controlling apparatus attracts its armature as a result of the closure of the above traced circuit, it grounds a conductor that has a branch 81 extending to apparatus associated with each of the operators positions. At each operators position there is a relay 92, the energization of which is effected by the grounding of the associated branch conductor 81, subject, however, to the control of resting contacts of an assoeiated relay 91 and of contacts 303 (1) of an associated sequence switch 300. The relay 91 andthe sequence switch 300 are in turn controlled by circuits that are responsive to the busy or idle condition of the associated position, as will hereinafter be explained. When. the position is unengaged, both of the above mentioned contacts included in the energizing path for the relay 92 are closed. When the position is engaged and not in condition to have a call extended to it, one or the other or both of these contacts are open. 55 operates and applies a ground to all of Therefore, when the relay the branch conductors 81, only such of the relays 92 will be energized as are associated with positions where the operator is free to attend to an extended call.

Each of the operators positions is reprein the selection-controlling apparatus 5G, by a group of three relays 77 93 and 94., and each also has an associated trip magnet, 20 for position 0 and 21 for position U. The relay 77 of elich group is under the direct control of thh associated position relay 92, the relay 92 in operating closing in its front contact and armature a circuit that ex tends from battery by wayof conductor and through the winding of the group relay 77 to ground. Thus, when relay is operated the result of the movement of a finder sequence switch 200 into position 5, it causes the operation of all of the group relays 77 that are associated with operators positionswhich are in condition to receive an extended call.

The path over which an actuated finder circuit controls the selection of an idle operators positiouis under the joint control or": the relays 77 of the corresponding groups. lhe energizing path is controlled in the armatures and back contacts of the relays 77 in series, each relay 77, in operating, disconnecting the conductor 141 from the relays 7 7 beyond it in the series and connecting the conductor with the relays 93 and 9% of the associated group. Thus, when the relay 5:) acts to bring about the energization of all of one relays 77 associated with unengaged operators positions, the energizing path by way of conductor 141 is prepared for the operation of the relays 98 and 94 corresponding to the first operators position in the series that is unengaged. The energizcircuit is not-closed, however, until the finder sequence switch 200 moves out of position 6.

Gil

' The movement of the finder sequence switchQOO out of position 6 depends upon the closure of a circuit that extends from battery through the left-hand Winding of relay 30-, sequence switch contact 209 (6) of the associated finder circuit, sequence switch contact 209 (9 to 4) of finder circuit F, conductor 76, outer armature and back contact of relay 54, right-hand back contact and armature of relay 61 to ground. The closure of this circuit is therefore dependent upon the condition of the sequence switches of the associated finder circuits and of the relays and 61 that form part of the selection-controlling mechanism SC. When the relays 5i and 61 are inert and the sequence switches of the other associated finder circuits are in any of their positions from 9 to 4 inclusive, the circuit traced above is completed and the relay 30 is energized. The relay 30. in opcrating, closes a circuit that extends from battery through the motor magnet and cam 202 (6) cl toe sequence switch 200, righthandfront contact and armature of relay 30, and sequence switch contacts 208 (18 to 14;) and {2 to 7) to ground. The closure of this circuit moves the sequence switch out off position 6. moment after the sequence switch 200 moves out of position 6, it closes a circuit that extends from battery through the left-hand armature and back contact of the relay 5 associated with the first operators position in the series that happens at the time to be unengaged (assumed in the present case to be the relay 95 at position 0). conductor 83, back contact and left-hand switch spring of the corresponding relay 93 of the selectioncontrolling apparatus, winding of that relay, winding of the associated relay 9%, right-hand switch spring and rest ing contact of relay 93, front contact and armature ot the associated relay 77, conductor 141, inner armature and front contact of relay 54 (which relay is energized by its inclusion in a branch of the path that is being traced), back contact and armature of relay S3 left-hand back contact and armature oi relay 61, conductor 73, and finder sequence switch contact 215 (6 to 8) to ground. The closure of this circuit energizes relays 93 and 94*, and relay 93. in operatin disconnects the windings of both relays 93 and 94 from the initial energizing path by way of the "front contact of the associated relay 7 and the back contact of the operators position relay 95, and includes them instead in a circuit that extends from battery by way of the winding of the relay 95, conductor 84, left hand armature and switch spring of relay 93, thence through the windings of both relays 93 and 94,- the right-hand switch spring and armature of relay 93. and to ground by way of the path already traced through the left-hand back contact and armature m relay ()1 and conductor 73. lhe closure of this path maintains the energizw tion of relays 93 and 94; independent of control by relay 77, and also causes the energization of the relay of the selected position, Relay 94. in operating, closes in its right-hand front contact and armature the energizing circuit for the corresponding trip magnet 20, hus setting the tripping mechanism for the release of the corresponding set of brushes when the cord selector moves up. In its left-hand front contact and armature, the relay 94- closes the energizing circuit 'ol' the common relay 63 of the SlBClJl.O1l-COI1- trolling apparatus. This relay, in operating, closes a circuit that extends from battery through the left-hand winding of the finder circuit relay 2-30, sequence switch contact 210 (7), conductor 72, front contact: and arma ture of relay 63 left-hand back contact and armature of relay G1 and to ground by way of conductor 73 and sequence S'W'fltCll contact 215 t to 8), Relay 30, in operating, close lllt) a circuit that extends from battery through I the motor magnet and cam 202 (7) of the to ground.

The closure of the above circuit moves the sequence switch 200 from position 7 to pe sition 8. In position 8, a circuit is closed that extends from battery through the up drive magnet 34 of the associated cord selector switch CS, conductor 89, sequence switch contact 207 (8 to 9), right-hand front contact and armature of relay 30, and se quence switch contact 215 (8 to 9) to ground. The relay 30 is at this time held energized as a result of a locking circuit by way of its right-hand winding that was completed when the relay was operated in position 7 of the sequence switch by the actuation of relay 63 of the selection-controlling apparatus, as previously described. This looking circuit extends from battery through sequence switch contacts 205 (2 to 9), right-- hand winding of relay 30, sequence switch contacts216 (7 to 9) and (2 to 9), left-hand front contact and armature of relay 30, and. to ground by way of the armature and back contact of relay 37. The up-drive magnet 34 remains energized and the upward movement of the cord selector CS continues as long as the relay 30 remains energized; and the continued energization of the relay 30 is under the control of relay 37 which governs the locking circuit of relay 30.

At the outset of the upward movement of the cord selector CS, the tripping levers 5 of all of the sets of brushes come into position to be engaged by their corresponding tripping yokes 7 and as it is the trip magnet 20 that in the present instance is energized, the set of brushes 2 is tripped and made active that is adapted to engage the. terminals of connecting circuits leading to the corresponding operators position 0. Immediately after the brush-tripping point is passed, a circuit is closed that releases the selection-controlling apparatus and moves the finder circuit sequence switch into its next position. This circuit extends from battery through the winding of relay 61, conductor 74, sequence switch contact 211 to 8), conductor and segment K of t e cord selector commutator and corresponding brush to ground. In operating,

. the relay 61 closes a locking circuit for itself by way of its left-hand front contact and armature, conductor 73 and sequence switch contact 215 (6% to 8) to ground. I It also opens, in its left-hand armature and back contact, the connection of the conductor 73 with the operated group relays 93 and 94 and the position relay 95 of the O operators position, which connection up to this time had been maintaining these relays energized.

switch of any of the finder circi conductor 75,. and right-hand front contact and. armature of relay 61 to ground. The closure of this circuit moves the finder circuit sequence switch from position 8 to position 9. As it moves out oi position finder sequence switch opens the locking circuit of relay 61, and, in reaching position 9, it closes in sequence switch contact 39 (9 to 4) the series path which is sum for moving out of position 6 the s ground has been reapplied to this path by way of conductor 7%; and FL g contacts of relays 54 and 61 in the role se of the last mentioned relay at the coinplet =1. of the selecting operation, the selection-corn trolling apparatus SC is again available for it} the use of any finder circuit that is read i extend a call.

After the cord selectonswitch CS es the brush-tripping posit'on, it continues its upward movement until the brushes stopped by engaging the terminals of one of the connecting circuits that is idle or unengaged. The idle or busy condition of the connecting circuit is indicated by the presence or absence of ground on the test terminal 118 of each connecting circuit. When the brushes engage the terminals or an. idle connecting circuit, a path for flow of current is completed from battery through the winding of the relay 3?, ser quence switch contact 206 (8 to conductor 99, brush 114, test terminal 18, con ductor 88, listening key sequence switch contact 406 (l) andback contact and armature of relay 420 to ground. Relay 3'? thereupon attracts its armaturean opens the previously traced locking circuit that has been holding relay 30 energized. Relay 30, in releasing its armatures, opens in its righthand front contact and armature, the energizing circuit for the up-drivc magnet 34, thus stopping the brushes of the cord selector switch in engagement with the ter minals of the selected connecting circuit. In engaging its back contact, the right-hand armature of relay 30 closes an energizing circuit for the motor magnet of the finder sequence switch, by way of cam 202 (9) and cam 215 (8 to 9), which moves the. sequence switch 200 out of position 9. The finder sequence switch then continues to move untilit reaches position 14, where the talking circuit is completed in cams 213 and 214.

An instant after the finder sequence Switch leaves position 9, it closes a circuit that extends from battery through the winding of relay 421 of the connecting circuit, listening key sequence switch contacts 407 (1), left-hand back contact and armature of relay 422, conductor 87, cord selector, switch terminal 117 and corresponding brus 113, conductor 98, and finder sequenc switch contacts 205 (9% to 14) and .(9a toll) to ground. Relay 4.21, in operating, closes a lockingcircuit for itself that extends byway of its left-hand front contact and armature, and sequence switch contact 405 (1 to 6) to ground. Relay 421 also closes a circuit that extends from battery through the motor magnet and cam 403 (1) of the listening key se uence switch and right-hand front contact an armature of relay 421 to ground. The closure of this circuit causes thelistening key sequence switch' to move out of position 1, and in doing so, to open the test conductor 88 in sequence switch contact 406 (1), thus making the connectingcircuit test busy, and also to open in Sequence switch contacts 407 (l) the path over which the relay 421 was first energized. I Associated with relay 421 is a relay 423 which is energized and locked up over the same path as relay 421. Relay 423, in operating, closes a circuit that extends from battery through the winding of relay 422 and front contact and armature of relay 423 to'ground. Asa result, relay 422, prior -to the moving of listening key-sequence switch out of position 1-, has disconnected conductor 87 from connection with battery by way of sequence switch contact 407 (1) and the windings of relays 421 and 423, and has connected it with an alternative path to battery by way of the left-hand front contact of relay 422 and the device 424. When the lismning key sequence switch reaches position 2, arf'addltional path to ground for holding therelay 422 energized is closed by Way of Sequence switch contact 412 (2 to 7).

.When the listening key sequence switch 400 is moved out of position 1, in the mannor described above, it continues its movement until it reaches position '7. In position 7,"the cams 408, 409, 410 and 411 of the listening. key'sequence switch interrupt the talking strands of the connecting circuit and include between their severed ends a loop that has connection by way of conductors 135 and 136 with the operators telephone. set 147. This .puts the operator in communication with the callingsubscriber. Uponv learning; the number of the line that is wanted;fthe operator may complete the connection .by inserting the calling plug 30 425, in which, in the present instance, the

. connecting circuit lishing connection between a connecting circuit and a telephone line may obviously be employed. In the present instance, the connection-extending means is represented as a cord circuit provided with a repeating coil 426, answering and calling supervisory relays 427 and 428, respectively, and a switch 429 for applying ringing current from the source 430 to ring the bell at the called subscribers station D. As all of these parts may have their usual functions and may op crate in, the usual way, a description of them and of the exact'ma'nner in which the cord circuit is organized is thought to be unnecessary.

When the calling plug 425 is inserted in 'thecalled line spring-jack, an energizing called line. The cut-ofi' relay 11 may have its usual functions of disconnecting the line relay 12 thus depriving the line of control over the calling apparatus. The relay 420, in operating, interrupts, at another point the path to ground ofthe test conductor 88. The relay 431, in its back contact, breaks the connection of the tip of the plug with, a conductor 133, which extends to the operators telephone apparatus and is used in connection with testing the called line be fore inserting the plug, and, in its front contact, closes the tip strand of the connecting circuit for talking purposes.

After the connection between. the calling line and the called line has been established, the operator may disconnect her telephone apparatus from the connecting circuit by pressing the key 432. This closes a circuit that extends from battery through the motor magnet and cam 402 (7) of the listening key sequence switch 400, and to ground by way of the closed contact of the key 432. The switch 433 is closed when the calling plug 425 is inserted, so that when the listening key sequence switch moves. out of position 7 as result of pressing key 432, the energization of relay 422 is maintained by, a path that extends through the right-hand front contact and armature of the relay and to ground by way of the closed contacts of switch 433.

lhe termination of the conversation between the subscribers is indicated in the usual way by signals displayed when the supervisory relays 427 and 428 become inert, and disconnection is e'fi'ected by opening switch 433. This interrupts the energizing circuit of relay 422, and that relay, in -re leasing its armatures, breaks the connection of conductor 87 with battery by way of the device 424. When current ceases to flow through conductor 87, the relay 300;? the finder circuit, which has been included in the path of current flowby way of con ductors 87, '98, 50 and 53 and finder sequence switch cams 205 and 212, releases its armatures. This closes the circuit from battery through motor magnet and cam 202 (8 to 14:) of the finder sequence switch, lefthand back contact and armature of relay 30 and armature and back contact of relay .37 to ground. This moves the finder circuit sequence switch from position 1 1 to position 15, Where a circuit is closed from battery through the motor magnet and cam 202 (15) of sequence switch 200,

rightehand back contact and armature of.

relay 30, and cam 215 (15) to ground. When the finder sequence switch reaches position 16 as the result of the closure oi the above circuit, a circuit is com pleted that directly or indirectly may cause the brushes of the switch LE to be disconnected from the terminals of the calling line. When this disconnection is efi'ected, a circuit may be completed that extends from battery through the motor magnet and cam 20 1 (16)- or" the finder sequence switch to ground. This moves the finder sequence switch 200 to position 17, in which position a circuit is closed that extends from battery through the down-drive magnet 35 of the cord selector switch. CS, conductor 90 and finder sequence switch contact 215 (17) to ground. This causes the return of the cord selector switch. When the switch reaches its normal position, it closes a circuit that extends from battery through the motor magnet and cam 20% (17) of the finder sequence switch, conductor 31 and segment Y of the cord selector commutator and corresponding brush to ground. This causes the return of the finder sequence switch 200 to its normal or 1 position; and from this position it is later moved through its 1., 2 and 3 positions by means of circuits controlled in finder sequence switch cams 202 and 203. These circuits are not concerned with the present invention and need not be described.

This restores the connecting circuit to its normal condition and renders it again available for selection by a cord selector.

As has been explained hereinbefore, the

selection-controlling apparatus SC includesa relay 77'for each of the operators positions to which the selection-controlling apparatus is adapted-to cause the cord selector switches to extend calls; and unless the cor responding .relay 77 is energized, a cord '92, by the operation ofthe common relay 55 when a selector switch is ready to extend the call, is in turn under the control of switches that are responsive to the engaged or unengaged condition of the corresponding operators position. The above mentioned switches, in the present instance are the cam 303 of the operators sequence switch 300 and the armature and. resting contact of the relay 91. One or the other or both of these switches is operated to open the energizingpath of the relay 92 whenever the operator's position is unavailable for receiving calls.

Thus, when the operators position has been selected by one of the call extending circuits, the position is rendered inaccessible to other call extending means. When the position is selected, the relay 95 is operated in a manner previously described. In operating, the relay 95 closes a circuit that extends from battery through the motor magnet and cam 302 (1) of the operators sequence switch, right-hand front contact and armature of relay 95, and right-hand front contact and armature of relay 125 to ground.

The relay 125 at this time is operated, as its energizing path is completed by way of local contacts 127 of the operators telephone ack 126 which contacts are closed when the operator is at her position and has her telephone plug inserted in the telephone jack. As a result of the closure of the circuit traced above, the operators sequence switch 300 is moved out of position 1, thus opening the energizing path of relay 92 in sequence switch contact 303 (1) and making the position unselectable.

The next resting position of the operators telephone sequence switch 300 is position 4; but as relay 125 is energized, the motor magnot has an energizing circuit in this position by wayof sequence switch contact 302 (4:) and the left-hand front contact and armature of relay 125 to ground, and, conse qucntly, the sequence switch moves on to its next resting position, 17. switch remains in position 17, keeping the operators position uuselectable, until at a later stage in the operation, the switch 192 is operated in any suitable manner, to close its contacts. At this time, a circuit. is closed that extends from battery through the motor magnet and cam 302 ('17) of the operators 11 5 The sequence 1 telephone sequence switch and closed conunselectable.

nected with one of the connecting circuits, the corresponding position is also rendered This is effected through the medium of the relay 91. ,W hen. the listening key sequence switch 400 of any of the connecting circuits of the operators position is moved to position '4" to bring the operators telephone set into connection with the corresponding circuit, an energizing path is completed that extends from battery through the winding of relay 91, conductor 13?, and listening key sequence switch contact 404 (2 to 9) to ground. The completion of this circuit causes the relay 91 to attract its armature and interrupt the path over which relay 92 is adapted to he energized, thus preventing the operation of the associated selec" hon-controlling relay '27,

the operatorstelephone jack 1% when the operator leaves her position, also renders the position unselcctable. When the plug is removed, the breaking of the local contact 152? causes relay 125 to become inert and release its armatures. This closes a circuit that can tends from battery through the motor mag" net, and cam 302(1) of the operators telephone sequence switch 390, and to ground by way of the left-hand back'contact and armature of relay 1:25. In moving out of position 1 as the result of the closure of this circuit, the sequence switch interrupts the energizing path for the relay 92 in sequence switch contact (1), thus preventing the operation of the corresponding selectioncontrolling relay '3 when a connection is to be extended.

The particular system herein iilus/rated and described includes several. features that are the inventions of others and th closed and claimed in other copenuing applications. This is in order that a clear understanding of the organization and operation of the preferred ernho' the present invention in": had, no intention of claimir-zig such other tures.

hat is claimed is:

l. The combination with switch hav a lurality of groups stationary t niia s and adapted for group indi lual terminal selection, of plurality oi e i: tors positions, a group of connecting cir cuits at each position, each of said grou v of circuits having connection with a con i spending group of switch terminals, selection-controlling apparatus controlling the group-selecting operation of said switch, a relay at each op ator s position, said relays cooperatingin the control of said selectioncontrolling apparatus, a normally open energizin circuit for each reay, and ans actuated in initiating call closing said energizing circuits of the relays at unengaged operators positions.

he removal of the telephone plug extending a call to any ofthe circuits of of said groups, apparatus for contra 7c the group-selecting operation of said swiandmeans made active in initiating a will for placing said apparatus under the control of said operators positions.

3. The combination with a plurality operators positions, of a switch for extend ing calls thereto, said switch having a new mally inactive brush for each operators p sition, a tripping magnet for each brasi: adapted when energized to make the corro so spending brush active, apparatus for con-- trolling the selection of a particular of said trip magnets for energization, means made active upon the initiation of for placing said apparatus under the con 8 trol of said operators positions, and means for energizing the selected tripping magnet.

4. The combination with a plurality of operators positions, of a group of conni ing circuits at each position, a switch extending a call to any connecting circuit of any of said positions, apparatus controh ling the group selection of said switch, a. switch at each operators position responsive to the busy or idle condition thereof, andv means made active in initiating a call placing said apparatus under the control o said operators position switches.

The combination with a plurality or? operators positions, of a switch for selecting the same to extend calls thereto, a corrc spending plurality of magnets associated with said switch, means actuated by each said magnets when energized to cause said switch to extend a call to the correspond operators position, means made operativ in initiating a call for selectin one of s magnets for energization, and means mar operative thereafter "for energizing said looted magnet. a

G. The combination with a switch responding plurality of normally. inset brushes, of a magnet for each brush, me: actuated by each of said magnets when en' glued for rendering active the correspoi i-ng brush, a circuit terminating in s brushes, groups of circuits connected respcw tively with said groups of terminals, means under the control of said first-mentioned cir- 1 2o cuit for causing the selection of one of said magnets for energization, and means made operative thereafter for energizing said selected magnet. v

7. The con'ihination with a call-extending switch having a plurality of groups of terminals and a corresponding plurality of normally inactive brushes, of a magnet to each brush, means operated in the energi tion of each magnet for making the cor.

spomiing brush active, a plm'ality of operator; positions each having a group of conum'ling circuits terminating on a correhptllilllllg group of terminals on said switch, switching mechanism associated with each ogciaioifis position and rcsgonsive to the ened, on unenga god. c mcliti0n thereof, non wally inactive selecti m-controlling apparatus, means actuated in initiating a call for piacing Silitl apparatus under the control of said switching mechanisms, and energizing circuits for said magnets controlled. by said apparatus, said apparatus acting to 'cause the cnei gization of a single one of the magnets corresponding With an operators position that at the time is unengaged.

In Witness whereof, I hereunto subscribe iny name this 3rd day of July, A. '11, 1916.

FRANKLIN A. STEARN, 

